1. Field of the Invention
This invention relates to an improved electrode having a porous nickel surface. More particularly, it relates to a paste composition that can be used to coat a substrate and a process that results in a nickel supported porous nickel coated electrode useful as a cathode in water or brine electrolysis cells.
2. Prior Art
It is well-known that an active porous nickel surface can be produced by selectively dissolving a soluble component such as aluminum or zinc from an alloy of nickel and the soluble component. Such porous nickel and the alloy from which it is produced are frequently referred to respectively as Raney nickel and Raney alloy, named after their inventor. Several specific methods for producing Raney nickel and a variety of uses for this material have been suggested in the past. In U.S. Pat. No. 4,049,580, Oden et al., a method is suggested for making a supported Raney nickel catalyst by coating a nickel substrate with aluminum or aluminum nickel alloy. This process produces a thick layer of NiAl.sub.3 on a nickel substrate. Said layer is a precursor of a Raney nickel catalyst. The inventor suggests in column 1, lines 30-34 that the production of Ni.sub.2 Al.sub.3 as a surface coating is undesirable. In contrast I have found as set forth in my U.S. Pat. No. 4,116,804 that an improved electrode having a porous nickel surface can be formed by a process which includes the interdiffusion of aluminum and nickel at temperatures of at least 660.degree. C. to form a nickel aluminum alloy (Ni.sub.2 Al.sub.3) layer from which aluminum is subsequently selectively dissolved. This electrode, when used as a cathode in an electrolytic cell for producing hydrogen, chlorine and caustic from brine, exhibits exceptionally low hydrogen overvoltage.
Dickenson et al., U.S. Pat. No. 3,408,231, also discloses a method of making a negative electrode by forming a layer of nickel aluminide (Ni.sub.2 Al.sub.3) and then dissolving out the diffused aluminum with a caustic solution. Although many of the prior art electrodes formed from Raney nickel catalysts are good cathodes, I have continued to search for an electrode that can be inexpensively produced, has outstanding mechanical strength so as to have a long useful life and reduces power consumption in a chlor-alkali plant because of low hydrogen overvoltage.